1. Field of the Invention
This invention relates to methods and apparatus used in the treatment of an orthodontic patient. More particularly, the present invention is directed to methods and apparatus for selecting an orthodontic brace made of one or more components that have been chosen to facilitate achieving a particular objective as determined by the practitioner.
2. Description of the Related Art
Orthodontia is a branch of dentistry that prevents or treats irregular positions of the teeth. Teeth that are not in correct positions may hinder proper chewing of food, and may also tend to develop caries or contribute to gum disease. Furthermore, malpositioned teeth may present an unsightly appearance, especially if located in front or anterior portions of the patient's oral cavity.
An orthodontic brace is a device used to move teeth to orthodontically correct positions along the dental arch. Typically, the orthodontic practitioner will create a custom orthodontic brace for each patient by selecting components that apply gentle pressure to the teeth in certain directions. Over a period of time, the teeth tend to slowly shift toward desired positions. After an extended period of time, the growth of new bone tissue in areas next to the roots of the teeth will firmly hold the teeth in their new positions.
One type of orthodontic brace that is in widespread use comprises a set of orthodontic appliances along with an archwire. The appliances typically include a number of small, slotted brackets, each of which is mounted on a corresponding tooth along the dental arch. An archwire is received in the slot of each bracket and forms a track to guide the teeth toward desired positions. Usually, a set of appliances and an archwire are provided for both the upper and the lower dental arch of the patient, and treatment of both arches is carried out at the same time.
Today, there are numerous methods for selecting orthodontic appliances and archwires, and the particular selection method used by practitioner is related to the type of orthodontic techniques that are expected to be employed during the course of orthodontic therapy. For example, one popular technique is known as the “straight wire” technique, and involves the use of brackets having slots that are designed to be in a common plane once the teeth have moved to desired, final positions. Although the slots of the brackets are not aligned at the beginning of treatment due to the various malpositions of the teeth, the inherent resilience of the archwire provides a restoring force that tends to move the archwire and hence the slots of the associated brackets into alignment in a common plane.
In the straight wire technique described above, each of the selected brackets has a certain “prescription” that represents particular characteristics of the bracket. The prescription can include numerous different aspects or features of the bracket, such as the size of the archwire slot, as well as orientation of the slot relative to a base of the bracket that is intended to be mounted on the tooth surface. The prescription describing the orientation of the archwire slot relative to the base may include values for torque, angulation and rotation. In terms of tooth movement, “torque” is often described as tipping movement of the long axis of the tooth in a buccolabial-lingual direction (i.e., in directions toward and away from the patient's lips or cheeks and the patient's tongue), “angulation” is often described as tipping movement of the long axis of the tooth in mesial and distal directions (i.e., in directions toward and away from the center of the patient's dental arch) and “rotation” is often described as rotational movement of the tooth about its long axis.
The prescription of orthodontic brackets often varies from tooth to tooth. For example, many practitioners prefer that the long axes of the lower anterior teeth be as upright as possible, and consequently will prescribe for those teeth a bracket having torque and angulation values that are relatively small. In contrast, the upper central incisor teeth normally have long axes that are slanted. As a result, the practitioner will prescribe upper central brackets having torque and angulation values that are somewhat greater. However, the desired prescription may change from one orthodontist to the next. Moreover, in some instances the prescription is varied from the practitioner's normal practice in order to accommodate the initial position of a tooth, the location of adjacent teeth or the orientation of opposing teeth for a particular patient.
Another type of orthodontic brace is known as a positioner, and comprises an elastomeric material that is formed in the shape of a tray. The tray has a series of adjoining cavities for receiving the teeth. Each tooth is received in a respective cavity, and the resilient nature of the elastomeric material tends to shift the teeth to desired positions. An example of an orthodontic positioner is described in U.S. Pat. No. 5,055,039.
Orthodontic positioners are often made in the laboratory from a sheet of elastomeric material. One method of making a positioner includes an initial step of making an impression of the patient's dental arch using an impression material. A model of the patient's existing dental arch is then made from the cured impression. Next, teeth of the model are cut away and repositioned in wax in desired orientations. The sheet of elastomeric material is then molded over the repositioned model teeth in order to create a custom tray. The elastic material is resilient and has inherent memory, but preferably is sufficiently stiff in order to exert gentle pressure on the teeth when the tray is placed over the patient's dental arch. The pressure by the tray on the teeth tends to shift the teeth toward desired positions over a period of time.
U.S. Pat. No. 5,975,893 describes a method for incrementally moving teeth using a series of polymeric trays in successive order. The trays are designed by a computer to provide a plurality of different, intermediate tooth arrangements as well as a final tooth arrangement. Each tray is sufficiently resilient to provide corrective forces in order to move the teeth in relatively small increments and toward the desired, final tooth arrangement.
In the past, orthodontic practitioners have often selected prescriptions for braces by their first-hand knowledge of past treatment results with other patients and by reviewing results reported in the literature. However, some patients present unique problems, and reference to techniques that have been satisfactorily used in the past may not be suitable for certain patient's in the future. For example, a force module may be desired in a particular instance to assist in moving the teeth, and the force module may affect the final positions of the teeth to such a degree that the prescription should be changed.
Moreover, the problem of selecting an orthodontic prescription is aggravated by the nature of orthodontic treatment because the results of treatment may not be apparent for some time. Tooth movement is carried out slowly during orthodontic therapy, in order to reduce the amount of pain experienced by the patient and also to give sufficient time for the bone to grow and fix each tooth in place in its new position. As a result, practitioners prefer to make certain that the prescription of the brace that is initially selected is satisfactory for moving the teeth to desired, final orientations.
In addition, it is sometimes difficult for practitioners to predict the effects of tooth movements when a change in the prescription of the brace is made. The problem of predicting tooth movement is compounded by the fact that the roots of the teeth are not visible in ordinary view. Furthermore, spatial cognition of tooth movement in three dimensions is difficult, especially when such tooth movement may be influenced by the positions of adjacent teeth along the dental arch.
As can be appreciated, it would be desirable to provide a system for facilitating the selection of a custom orthodontic brace, and in particular to provide a system for facilitating the selection of a prescription for a custom orthodontic brace. Preferably, such a system would be easy to use and would facilitate the understanding of long-term effects of the particular brace selected. Moreover, such a system should be adaptable for use with any type of brace, including positioners, a series of custom trays, systems that include brackets and archwires as well as other types of braces.